There are many studies that document adult immigrants and language attrition. Those who experience the most attrition are the ones who fully integrate - they en

There are many studies that document adult immigrants and language attrition. Those who experience the most attrition are the ones who fully integrate - they entirely cease using their native language and eventually shift their dominant language to the new one. Even then, attrition doesn't result in complete ("true") language loss. First, there is a decline in vocabulary, and eventually a loss of accurate phonology so that native listeners no longer judge them to be native speakers. However, they generally retain the ability to comprehend and communicate in their native language, even if they haven't used it for many years. The point is simply that it is VERY difficult to completely lose your native language as an adult, assuming it was your dominant language throughout childhood.